A method for measuring a shape of a reflector surface of a
heliostat at night using a
bright star at different elevation and azimuthal settings according to an embodiment of the current invention includes setting the
heliostat in fixed orientation such that aberrated and overlapping star images formed are translated due to Earth's rotation in a translation direction across the
heliostat array
receiver; viewing images of the
bright star using a fixed array of cameras placed at or near an array
receiver of the heliostat, wherein each camera of the fixed array of cameras has a
large aperture lens, and simultaneous exposures are made quickly enough and repeated for long enough, so that, as they translate past the cameras, the aberrated star image is fully sampled in two dimensions, and wherein every point on the reflector surface of the heliostat appears in one or more of the recorded images as being bright from reflected
starlight; and
processing the recorded images from the fixed array of cameras with a data processor to obtain the
surface shape by integration of the surface slopes.